The present invention relates generally to the field of composite materials and, more particularly, to composite materials used for heating products. The art has seen failed or inadequate efforts for attaining highly stable, highly uniform electric heating performance. There is the need for efficient means to provide heat using electricity. Unlike other heating means such as hot air, hot water, thermal oil, or steam, which all require significant capital and equipment, such as boilers, pipes, ductwork, and controls, electrical resistive heating only requires simple circuitry to connect a heating element to the power source and for control.
Most electrical heating equipment is large and requires resistive wires, insulation and high voltages. Examples include electrical blankets with wires and mesh conductors embedded in materials or sandwiched in laminates. Insulated resistive wires are not sufficiently flexible and can break with repetitive flexing. As resistive wires are heated, resistance drops and the temperature increases if the voltage is held constant. To control the temperature state of the art system often require a power control with a feedback from a thermostat or like sensor. This equipment causes concern over sparks and consumer safety. For example, heated seats in vehicles have been the subject of lawsuits and warranty failures because of overheating or wire breakage. In addition, danger of electrocution and burning exists when using electric blankets and heating pads, which are hazardous when the wires are exposed to a conductor.
U.S. Pat. Nos. 6,974,935 and 6,814,889 to Inditherm PLC discuss large area stand-alone carbonaceous films, films coated on substrates or embedded in insulating layers, and laminate forms. One goal of thin planar larger area products is to enhance uniformity of the heating effect, increase safety, operate at low voltage, maintain temperature constant at a given voltage and improve reliability and efficiency of the heating system. In practice the goals were inadequately realized. The goals were realized inadequately in practice of the processes and products described in the patents.
The present invention provides composite materials and products incorporating the materials with enhanced heating uniformity, increased safety, improved reliability and efficiency, as well as methods of making the materials and products that effectively deliver the advantageous properties and performance.